A large percentage of the population suffers from IgE-mediated allergies. Many of those patients suffer from allergic reactions against several antigens. A high percentage of these allergic reactions are caused by plant allergens, particularly pollen from anemophilous (i.e., “wind loving”) plants. Among North American plants, the most prolific producers of allergenic pollen are weeds, primarily ragweed, though sagebrush, redroot pigweed, lamb's quarters, Russian thistle (tumbleweed), and English plantain are also important. Grasses and trees are also primary sources of allergenic pollens. Although there are more than 1,000 species of grass in North America, only a few produce highly allergenic pollen. These are mostly summer grasses, examples of which include timothy grass, Kentucky bluegrass, Johnson grass, Bermuda grass, redtop grass, orchard grass, and sweet vernal grass. Examples of trees that produce allergenic pollen include members of the birch, oak, ash, elm, hickory, pecan, box elder, and mountain cedar families. Allergy to pollens from birch and related trees (alder, hazel), are quite prevalent in Northern and Middle Europe, North America, and certain parts of Australia and Asia.
The symptoms of allergy, such as allergic rhino conjunctivitis, asthma, dermatitis, hay fever, hives and even anaphylactic shock, arise from the interaction between antibodies and allergens, more particularly IgE recognition of allergens. In particular, IgE molecules bind to an allergen, for example, a plant pollen. The tail region of the IgE molecule, i.e., the Fc part, binds to Fc receptors that are mainly located on the surface of mast cells in tissues and basophils in the blood. Antigen binding triggers the mast cells or basophils to secrete a variety of cytokines and biologically active compounds, especially histamine. These molecules cause blood vessels to dilate and become leaky which in turn helps white blood cells, antibodies and complements components to enter sites of reaction. Those molecules are on the other hand largely responsible for the symptoms of allergic reactions. There are different degrees of allergic reactions which range from slight itching of the eyes and the symptoms of a slight cold over severe pains to live-threatening symptoms like anaphylactic shock which may occur for example after the sting of a bee.
While drug therapy may reduce the symptoms of an allergic response, only allergen-specific immunotherapy (ASIT) can serve to avoid the allergic reaction and thereby effectively “treat” allergic disorders. ASIT is based on the administration of a small amount of a disease-eliciting allergen to the patient in order to induce antigen-specific nonresponsiveness. More particularly, the administration of a small amount of antigen leads to the production of allergen-recognizing IgG antibodies or “blocking antibodies”. These so-called blocking antibodies largely inhibit contact between the allergen and the IgE molecules present in the patient's body; thus, the reaction between the allergen and the mast cells mediated by IgE molecules is largely avoided.
In the field of allergen-specific immunotherapy (ASIT), different allergy vaccines have been developed. Previously, these vaccines simply consisted of small amounts of the native allergen or natural allergen extracts to be applied to the patient. However, with the development of genetic engineering, vaccines based on recombinant allergens have been produced. A major disadvantage of such allergen-containing vaccines is that the application of such vaccines causes in the patient unwanted side-effects. If, for example, the allergen against which the patient is allergic is applied subcutaneously to the patient an unwanted side-effect like itching up to anaphylactic shock can occur since the IgE antibodies present in the patient's body react with the allergen and cause the allergic reaction.
In an effort to overcome the undesired side-effects of conventional immunotherapeutic agents, hypoallergenic allergens, i.e., allergens having reduced allergenic potential as compared to their naturally-occurring counterparts, are eagerly sought.